Study of User Interruptibility Estimation
Based on Focused Application
Switching
Takahiro Tanaka

Abstract

Tokyo University of Agriculture andIn this study, we propose a user-interruptibility
estimation method based on focused application
switching (AS) during PC work. It was experimentallydemonstrated that the interruptions of AS are more
acceptable than those during continuous work.
Therefore, we constructed an algorithm that estimatesthe interruptibility of AS at three levels based on 19
selected indexes. The feasibility of the interruptibility
estimation of AS was demonstrated by an estimationexperiment using another dataset of 11 users.

TechnologyNaka-machi 2-24-16, Koganei-shi,
Tokyo, Japan
takat@cc.tuat.ac.jp
Kinya Fujita
Tokyo University of Agriculture andTechnology
Naka-machi 2-24-16, Koganei-shi,
Tokyo, JapanKeywords

kfujita@cc.tuat.ac.jp

interruptibility, breakpoint, application switching

ACM Classification Keywords
H5.2 [User Interface]: Theory and methods. H5.3
[Group and Organization Interfaces]: Computersupported cooperative work.

General Terms
TheoryCopyright is held by the author/owner(s).

Introduction

CSCW 2011, March 19–23, 2011, Hangzhou, China.

In recent years, the possibility that users areinterrupted by information systems has been increasingalong with popularization of the Internet and theACM 978-1-4503-0556-3/11/03.

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ubiquitous computing environment. However, thetiming of interruptions has not been controlled in mostsystems. Preceding studies [1] have shown thatfrequent interruptions that do not reflect the user
status can fragment the user’s working time anddecrease intellectual productivity.
In this study, we consentrated on focused application
switching (AS) that is change of using application,
which is considered to be not only the breakpoint of PCwork, but also of intellectual activity. We present theexperimental data and propose an interruptibilityestimation rule for AS.

Idea
There are several studies that aim to estimate the user
status using various techniques such as counting
keystrokes or mouse clicks and using various sensors
that are set in the living space or on the users [2-4].
These methods are expected to adequately estimate
the user status by observable physical activity indexes.
However, intellectual activity such as deep thinking has
no observable output. On the other hand, some studies
reported the relationship between interruptibility andthe breakpoint of the work [5-7]. At the breakpoint, theuser’s interruptibility is expected to increase
instantaneously, even if the task requires intellectualactivity. Furthermore, it was suggested that thebreakpoint level affects interruptibility [5]. A taskstructure which categorized operations analysis is thus
required to determine this level. The multi-tasking
aspect of PC usage also makes it potentially difficult toapply the task-structure-based method. Therefore,
distinguishing the interruptibility level of a breakpoint
remains challenging [7].

We concentrated on focused application switching as abreakpoint in PC work, which is a transition of theactive application window. AS is considered to be theuser’s intentional switching of his working space orworking target. Therefore, the user’s concentration at
AS is expected to be instantaneously weakened
compared to that during continuous work. Moreover,
AS commonly and frequently occurs in PC work, and iseasily detected, which implies that AS is a potential
source of information presentation with low risk of task
disturbance.

Experiment I: Selection of Indexes
To examine the assumption, we experimentallycollected PC operation records and subjective interruptevaluation logs and analyzed them. Figure 1 shows thelogging tool we developed that records user operations
at every 500 ms. The tool interrupts subjects at
automatically selected AS, or every five min duringcontinuous work (NAS), and requires the users to
subjectively evaluate interruptibility, which means if
and how they want to be interrupted. The scores wereFigure 1.Experimental logging system.

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Table 1. Subjective interruptibility scores at AS vs. NAS.

Subjective Interruptibility

Freq.

Ave.

131841

3.2

33

301

2.8

123

45AS

97

144

206

263

NAS

58856362

scaled from “1: Absolutely uninterruptible” to “5: Noproblem.” The evaluation logs, which consist of 40 setsof daily 1-h PC activity, were collected from 10university students, who did their own tasks such asdata arranging, programming, writing report and so on.
ResultTable 1 shows an interruptibility comparison between
AS and NAS, including the frequencies and averages.
The experimental results demonstrate that theinterruptions of AS are significantly more acceptable forusers than those during continuous work (p < 0.01, ttest). However, information systems must distinguishthe more interruptible AS based on acquired
information. Therefore, we analyzed the relationshipbetween the interruptibility scores and indexes from theoperation records.
Interruptibility-Estimation Rule
In general, the opening of an application window is
considered to be the beginning of a new task, while its
closure the end. This type of index is expected toreflect the discontinuity of work. The close coupling oftasks that are performed in two focused applications
may make AS uninterruptible. The indexes that mightreflect the application coupling such as “copy andpaste” was also examined. Furthermore, physicalactivities, such as keystrokes and mouse operations,are expected to reflect interruptibility as reported in [2].

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Therefore, we analyzed over 12 h of operation records
using the above three viewpoints.
From this analysis, we selected 19 indexes with anexample shown in Table 2. We investigated a cooccurrence relation among 19 indexes to define theestimation rule. It was anticipated that the effect of theindexes varies with situations such as the beginning,
the end, and the continuity of the task. Therefore, wedivided ASes and defined estimation rules according to
the three situations based on the number of windows
opened as increased, decreased, and no change afterAS. We compressed the interruptibility into threelevels: interruptible, neither, and not interruptible, fromthe practical viewpoint. Scores 4 and 5 were converted
to High, score 3 was converted to Medium, and scores
1 and 2 were converted to Low interruptibility.

Experiment II: Evaluation
We evaluated the interruptibility-estimation rule of AS
using recently collected 50-h log data from 11
university students, and the results using our method
are shown in Table 3. The precision of highinterruptibility was 54% and the probability that theestimated error is ≤ 1 was 88%.

Discussion
By the results of the evaluation, the precisions of highand low interruptibility were both 54%, and theaverage of the three levels was 44%. Although theproposed method did not provide accuracy, itdemonstrated the feasibility for estimating highlyinterruptible, implying the chance to interrupt, AS at
more than 50% precision. In addition, the precision
improves almost to 90% if the user allows interruptions
at a moderate interruptibility level. The high-riskTable 2. Examples of indexes affecting interruptibility at AS.
id

Table 3. Results of interruptibility estimation on evaluation.
EvaluatedIndexesGroup 1: Work discontinuity
C

Increase of opened window compared to avg. of last 2 min.

D

Decrease of opened window compared to avg. of last 2 min.

EWindow message (quit).

Group 2: Application couplingF

Window message (clipboard).

G

Parent-window to child-window transition.

I

Reuse of the same application within 2 min.

Estim
ated

Precision

RecallError≤ 1LowMedHigh

High

1644

69

0.54

0.22

0.88

Med294

159

192

0.25

0.60

1.00

Low

135

63

53

0.54

0.30

0.79

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[2] S. Honda et al., A home office environment basedon the concentration degrees of workers: A virtual
office systemvalentine. Trans. Info. Processing Societyof Japan, 39(5) (1998), 1472-1483 (in Japanese).

Group 3: Physical activity
N

Continuous use of one application over 2 min.

P

Typing activity within 20 s before AS.

RMore than 10% operating time in the last 2 min.

estimation rate, which is the misestimation of low
interruptibility ASes to high ones, was 16 cases and1.6% of the entire ASes. The proposed method appears
to allow information systems to reduce the risk ofserious work disturbance by interruption. The otherfeatures of this method, which could serve as practicaladvantages, are: 1) it works without any sensors and2) the estimation rule requires no restriction in PC
usage. We need to improve the rule to estimate thehighly interruptible ASes with greater accuracy.

Conclusion
We experimentally confirmed that application switchingis a relatively good opportunity to interrupt PC work.
Furthermore, we proposed an interruptibility-estimation
rule and demonstrated the feasibility of the estimation.

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